The present invention relates to an A/D conversion device having a tuning function and an A/D converter error correction device for realizing the tuning function of an A/D converter.
In recent years, the number of systems for converting an analog signal into a digital signal and conducting fine control based on a micro change in the digital signal increases. A system of this type requires a high accuracy A/D converter or a high resolution A/D converter. Normally, if device technology develops and a device becomes small in size, it becomes difficult to control a reference transition voltage related to the A/D converter. To manufacture a high accuracy A/D converter, however, it is necessary to suppress fluctuation in this reference transition voltage.
Further, the resolution of an A/D converter is normally fixed and various resolutions cannot be provided to a single A/D converter. Due to this, to manufacture a high accuracy A/D converter, it is necessary to prepare an A/D converter having a resolution required by a system for each resolution.
FIG. 1 is a block diagram showing the configuration of a conventional A/D conversion device for obtaining a highly accurate digital converted value. As shown in FIG. 1, this A/D conversion device is constituted so that an analog input voltage is amplified by an amplifier 11, the amplified voltage is subjected to A/D conversion by an A/D conversion circuit 12, and the obtained digital converted value is supplied to, for example, a central processing unit or CPU 13.
FIG. 2 is a block diagram showing another configuration of a conventional A/D conversion device for obtaining a highly accurate digital converted value. As shown in FIG. 2, this A/D conversion device is constituted so that an analog input voltage value is converted into a digital value by an A/D conversion circuit 16, the digital converted value is subjected to an error correction using a correction value stored in a register 18 by an arithmetic section 17 and a digital output value is thereby obtained. Each of the A/D converters 12 and 16 employed herein as shown in FIGS. 1 and 2 includes, as an analog voltage comparison circuit, resistors and capacitors as many as bits according to resolution.
The A/D conversion device wherein an analog input voltage is amplified and then subjected to A/D conversion has disadvantages in that an error occurs to the analog voltage value when the analog input voltage value is amplified by the amplifier and that an error derived from fluctuation in the reference transition voltage of the A/D conversion circuit 12 occurs.
Furthermore, the A/D conversion device wherein a digital converted value is subjected to arithmetic operation to correct an error has a disadvantage in that it takes long time to obtain error corrected data since each digital converted value is subjected to an arithmetic operation. Besides, since the resolution of the A/D conversion device is determined according to the number of resistors and capacitors mounted on the A/D conversion device at the time of manufacturing the conversion device, A/D conversion cannot be performed with the fixed resolution and varied resolutions cannot be, therefore, obtained with a single configuration.
It is an object of the present invention to provide an A/D conversion device which can dispense with an amplifier for amplifying an analog input voltage and an arithmetic circuit for performing an error correction arithmetic operation and which has a function to correct an error derived from fluctuation in a reference transition voltage unique to a product.
It is another object of the present invention to provide an A/D converter error correction device for realizing a function to correct an error derived from fluctuation in a reference transition voltage unique to a product. It is still another object of the present invention to provide an A/D conversion device for realizing an A/D converter having a high resolution.
FIG. 3 is a principle view which shows the configuration of a high accuracy A/D conversion device according to the present invention. This A/D conversion device is constituted as follows. As shown in FIG. 3, a zero transition voltage is inputted, as an analog input, into an A/D converter 21 and a digital converted value obtained by the A/D converter 21 is fed back to a device fluctuation correction circuit 23 by a feedback circuit 22. Likewise, a full transition voltage is inputted into the A/D converter 21 and an A/D converted value obtained by the A/D converter 21 is fed back to the device fluctuation correction circuit 23. Then, the error of the full transition voltage is converted into an analog voltage through a full transition voltage correction D/A converter 24 and the resultant analog voltage is supplied, as an H (a high) side reference voltage AVRH, to the A/D converter 21.
Likewise, the error of the zero transition voltage is converted into an analog voltage by D/A converter 25 for correction of the zero transition voltage and the resultant analog voltage is supplied, as an L (a low) side reference voltage AVRL, to the A/D converter 21. By doing so, it is possible to correct the error of the full transition voltage and the error of the zero transition voltage and to thereby improve the accuracy of the A/D converter 21.
FIG. 4 is a principle view which shows the configuration of a high resolution A/D conversion device according to the present invention. This A/D conversion device is constituted as follows. As shown in FIG. 4, first, an analog input voltage value is converted into a digital value by an A/D converter 31 while setting the H side reference voltage AVRH of the A/D converter 31 at a power source voltage Vcc and the L side reference voltage AVRL thereof at 0 V. The obtained A/D converted value is fed back to a high resolution corresponding circuit 36 by a feedback circuit 32, the A/D converted value thus fed back is stored in the internal register or the like of the circuit 36 and it is determined whether the analog input voltage is not less than xc2xd Vcc or not more than xc2xd Vcc.
If the analog input voltage is not less than xc2xd Vcc, the high resolution corresponding circuit 36 controls the output of an AVRL adjustment D/A converter 35 and raises the L side reference voltage AVRL to xc2xd Vcc. On the other hand, if the analog input voltage is not more than xc2xd Vcc, the high resolution corresponding circuit 36 controls the output of an AVRH adjustment D/A converter 34 to decrease the H side reference voltage AVRL to xc2xd Vcc. As stated above, after the difference between the H side reference voltage AVRH and the L side reference voltage AVRL is decreased to half the original difference, A/D conversion is carried out again, thereby making it possible to carry out the A/D conversion with a resolution twice as high as the original resolution.
This operation is repeated by a desired number of times. Then, an additional digital value stored in the high resolution corresponding circuit 36 is assumed as a significant bit value, the digital converted value obtained in the A/D converter 31 is assumed as a less significant bit value and the significant bit value and less significant bit value are merged with each other by a merge circuit 37 to thereby obtain a digital converted value having a desired number of bits. It is noted that the number of times of repetition of A/D conversion with a resolution twice as high as the original resolution is set by a counter or the like included in the high resolution corresponding circuit 36. By doing so, it is possible to perform A/D conversion with a desired resolution and to thereby realize an A/D converter having a higher resolution.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.